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        <figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">alert(&apos;Hello World!&apos;);</span><br></pre></td></tr></table></figure>
<h2 id="apply-和-call-的区别"><a href="#apply-和-call-的区别" class="headerlink" title="apply 和 call 的区别"></a>apply 和 call 的区别</h2><ul>
<li>ECMAScript 规范给所有函数都定义了 call 与 apply 两个方法，它们的应用非常广泛，它们的作用也是一模一样，只是传参的形式有区别而已。</li>
</ul>
<h3 id="apply"><a href="#apply" class="headerlink" title="apply( )"></a>apply( )</h3><a id="more"></a>
<blockquote>
<p>apply 方法传入两个参数：一个是作为函数上下文的对象，另外一个是作为函数参数所组成的数组。</p>
</blockquote>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">var obj = &#123;</span><br><span class="line">    name : &apos;denton&apos;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">function func(firstName, lastName)&#123;</span><br><span class="line">    console.log(firstName + &apos; &apos; + this.name + &apos; &apos; + lastName);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">func.apply(obj, [&apos;A&apos;, &apos;B&apos;]); // A denton B</span><br></pre></td></tr></table></figure>
<p>可以看到，obj 是作为函数上下文的对象，函数 func 中 this 指向了 obj 这个对象。参数 A 和 B 是放在数组中传入 func 函数，分别对应 func 参数的列表元素。</p>
<h3 id="call"><a href="#call" class="headerlink" title="call( )"></a>call( )</h3><blockquote>
<p>call 方法第一个参数也是作为函数上下文的对象，但是后面传入的是一个参数列表，而不是单个数组。</p>
</blockquote>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">var obj = &#123;</span><br><span class="line">    name: &apos;denton&apos;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">function func(firstName, lastName) &#123;</span><br><span class="line">    console.log(firstName + &apos; &apos; + this.name + &apos; &apos; + lastName);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">func.call(obj, &apos;C&apos;, &apos;D&apos;); // C denton D</span><br></pre></td></tr></table></figure>
<p>对比 apply 我们可以看到区别，C 和 D 是作为单独的参数传给 func 函数，而不是放到数组中。</p>
<p>对于什么时候该用什么方法，其实不用纠结。如果你的参数本来就存在一个数组中，那自然就用 apply，如果参数比较散乱相互之间没什么关联，就用 call。</p>
<h2 id="apply-和-call-的用法"><a href="#apply-和-call-的用法" class="headerlink" title="apply 和 call 的用法"></a>apply 和 call 的用法</h2><h3 id="改变-this-指向"><a href="#改变-this-指向" class="headerlink" title="改变 this 指向"></a>改变 this 指向</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line">var obj = &#123;</span><br><span class="line">    name: &apos;denton&apos;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">function func() &#123;</span><br><span class="line">    console.log(this.name);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">func.call(obj); // denton</span><br><span class="line"></span><br><span class="line">// 我们知道，call 方法的第一个参数是作为函数上下文的对象，这里把 obj 作为参数传给了 func，此时函数里的 this 便指向了 obj 对象。</span><br><span class="line">// 此处 func 函数里其实相当于</span><br><span class="line"></span><br><span class="line">function func() &#123;</span><br><span class="line">    console.log(obj.name);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h3 id="借用别的对象的方法"><a href="#借用别的对象的方法" class="headerlink" title="借用别的对象的方法"></a>借用别的对象的方法</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">var Person1  = function () &#123;</span><br><span class="line">    this.name = &apos;denton&apos;;</span><br><span class="line">&#125;</span><br><span class="line">var Person2 = function () &#123;</span><br><span class="line">    this.getname = function () &#123;</span><br><span class="line">        console.log(this.name);</span><br><span class="line">    &#125;</span><br><span class="line">    Person1.call(this);</span><br><span class="line">&#125;</span><br><span class="line">var person = new Person2();</span><br><span class="line">person.getname(); // denton</span><br></pre></td></tr></table></figure>
<p>从上面我们看到，Person2 实例化出来的对象 person 通过 getname 方法拿到了 Person1 中的 name。因为在 Person2 中，Person1.call(this) 的作用就是使用 Person1 对象代替 this 对象，那么 Person2 就有了 Person1 中的所有属性和方法了，相当于 Person2 继承了 Person1 的属性和方法。</p>
<h3 id="调用函数"><a href="#调用函数" class="headerlink" title="调用函数"></a>调用函数</h3><blockquote>
<p>apply、call 方法都会使函数立即执行，因此它们也可以用来调用函数。</p>
</blockquote>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">function func() &#123;</span><br><span class="line">    console.log(&apos;denton&apos;);</span><br><span class="line">&#125;</span><br><span class="line">func.call(); // denton</span><br></pre></td></tr></table></figure>
<h2 id="call-和-bind-的区别"><a href="#call-和-bind-的区别" class="headerlink" title="call 和 bind 的区别"></a>call 和 bind 的区别</h2><p>在 EcmaScript5 中扩展了叫 bind 的方法，在低版本的 IE 中不兼容。它和 call 很相似，接受的参数有两部分，第一个参数是是作为函数上下文的对象，第二部分参数是个列表，可以接受多个参数。<br>它们之间的区别有以下两点。</p>
<h3 id="bind-发返回值是函数"><a href="#bind-发返回值是函数" class="headerlink" title="bind 发返回值是函数"></a>bind 发返回值是函数</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">var obj = &#123;</span><br><span class="line">    name: &apos;denton&apos;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">function func() &#123;</span><br><span class="line">    console.log(this.name);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">var func1 = func.bind(obj);</span><br><span class="line">func1(); // denton</span><br></pre></td></tr></table></figure>
<p>bind 方法不会立即执行，而是返回一个改变了上下文 this 后的函数。而原函数 func 中的 this 并没有被改变，依旧指向全局对象 window。</p>
<h3 id="参数的使用"><a href="#参数的使用" class="headerlink" title="参数的使用"></a>参数的使用</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">function func(a, b, c) &#123;</span><br><span class="line">    console.log(a, b, c);</span><br><span class="line">&#125;</span><br><span class="line">var func1 = func.bind(null,&apos;linxin&apos;);</span><br><span class="line"></span><br><span class="line">func(&apos;A&apos;, &apos;B&apos;, &apos;C&apos;);            // A B C</span><br><span class="line">func1(&apos;A&apos;, &apos;B&apos;, &apos;C&apos;);           // linxin A B</span><br><span class="line">func1(&apos;B&apos;, &apos;C&apos;);                // linxin B C</span><br><span class="line">func.call(null, &apos;linxin&apos;);      // linxin undefined undefined</span><br></pre></td></tr></table></figure>
<p>call 是把第二个及以后的参数作为 func 方法的实参传进去，而 func1 方法的实参实则是在 bind 中参数的基础上再往后排。</p>
<blockquote>
<p>在低版本浏览器没有 bind 方法，我们也可以自己实现一个。</p>
</blockquote>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">if (!Function.prototype.bind) &#123;</span><br><span class="line">    Function.prototype.bind = function () &#123;</span><br><span class="line">        var self = this,                        // 保存原函数</span><br><span class="line">            context = [].shift.call(arguments), // 保存需要绑定的this上下文</span><br><span class="line">            args = [].slice.call(arguments);    // 剩余的参数转为数组</span><br><span class="line">        return function () &#123;                    // 返回一个新函数</span><br><span class="line">            self.apply(context,[].concat.call(args, [].slice.call(arguments)));</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
      
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